Allokotosauria is a clade of early archosauromorph from the Middle Triassic to Late Triassic known from Asia, Africa, North America and Europe. Allokotosauria was first described and named when a new monophyletic grouping of specialized herbivorous archosauromorphs was recovered by Sterling J. Nesbitt, John J. Flynn, Adam C. Pritchard, J. Michael Parrish, Lovasoa Ranivoharimanana and André R. Wyss in 2015. The name Allokotosauria is derived from Greek language meaning "strange reptiles" in reference to unexpected grouping of early archosauromorph with a high disparity of features typically associated with herbivore.
History
Nesbitt
et al. (2015) defined the group as a
stem-based taxon containing
Azendohsaurus madagaskarensis and
Trilophosaurus buettneri and all taxa more closely related to them than to
Tanystropheus longobardicus,
Proterosuchus fergusi,
Protorosaurus speneri or
Rhynchosaurus articeps. Therefore, Allokotosauria includes the families
Azendohsauridae and
Trilophosauridae by definition, as well as the potentially more basal
Pamelaria which is closer to them than to other early archosauromorphs.
Pamelaria is the earliest known allokotosaur, dating to the
Anisian of
India. In 2015, azendohsauridae was represented by a single genus
Azendohsaurus known from the
Ladinian to
Carnian of
Africa, while trilophosaurids are mostly known from the
Carnian to
Norian stages of
North America,
England and potentially
European Russia,
though one member of the latter group,
Variodens inopinatus, is known from
Rhaetian.
Since then, new discoveries have led to an expansion in generic diversity in azendohsaurids, including such taxa as
Shringasaurus from
Anisian India
, and
Puercosuchus from
Norian North America
, both of which also expand the clade's biogeographical and biostratigraphic range. According to studies of
Arctosaurus material from
Cameron Island in Canada, the latter may have been an allokotosaurian because of the similarities with
Azendohsaurus due to the presence of a posterior ridge from the centrum to the diapophyses which extends from the diapophysis all the way to the posterior ventrolateral corner of the centrum. This ridge overhangs a deep groove in the lateral surface of the centrum.
Description and phylogeny
Allokotosauria is most notably characterized by wrinkled side surface of orbital border of the
frontal bone, expanded and hooked
quadrate bone head on the posterior side, and a prominent tubercle developed above to the glenoid fossa of the
scapula, although there are other unambiguous traits that differentiate it from other early archosauromorphs. Below is a
cladogram showing the phylogenetic relationships of Allokotosauria within
Archosauromorpha as recovered by Nesbitt
et al. (2015).
Ezcurra (2016) also recovered a highly supported Allokotosauria with the same topology (including only
Pamelaria,
Azendohsaurus madagaskarensis and
Trilophosaurus buettneri in his analysis), but noted that
Pamelaria is nearly as likely to represent a basal
azendohsaurid instead.
Sengupta et al. (2017) described a new azendohsaurid and recovered Pamelaria as an azendohsaurid.
Pritchard and Nesbitt (2017) found support for the inclusion of Kuehneosauridae within Allokotosauria.
